Method of manufacturing a hollow spindle

ABSTRACT

A method of manufacturing a hollow spindle, especially for the pivotal mounting of valve-actuating levers to control exhaust-and-intake valves of an internal combustion engine. The spindle has an outer tube, in the interior of which a shaped tubular body is fixed in order to form at least two liquid-carrying chambers. To form a chamber, the tubular body is provided with a cutout extending in the longitudinal direction. The tubular body is a shaped inner tube that, seen in cross-section, has an inwardly-curved region that makes a rounded and stepless transition to the circular region, and of the tubular body. At least the circular region is joined by virtue of its material to the outer tube.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of manufacturing a hollow spindle thatserves, in particular, as the mounting for valve-actuating levers thatcontrol exhaust-and-intake valves in an internal combustion engine.

2. Description of the Prior Art

A hollow spindle, specifically a rocker lever spindle of theaforementioned type, is known from DE 42 21 708 A1. This rocker leverspindle consists of an outer tube, in the interior of which a shapedtubular body is fixed. By means of the tubular body, which has alongitudinal rib, at least two and preferably three liquid-carryingchambers are formed. In a special embodiment (FIG. 2), the tubular bodyhas a roughly V-shaped cutout that extends in the longitudinal directionto form a chamber. The tubular body is pushed or pressed into the outertube and fixed in place by cam-type elevations or shapings on the mantleof the tubular body. A disadvantage of this design is that there is noassurance that the fixed position of the tubular body will be maintainedor that the chambers will remain sealed under operating conditions.Furthermore, the lengths that can be manufactured are limited, so thatproduction costs are high.

U.S. Pat. Nos. 3,863,328 and 4,125,924, disclose a method for fittingtwo tubes together in a rattle-proof fashion. After one tube is slippedinto the other with a certain diameter clearance, a drawing point isformed on one end of the tubes. The tubes are then cold-drawn one atopthe other.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method formanufacturing a hollow spindle, particularly for the pivotal mounting ofvalve-actuating levers, in which the fixed position and the sealing ofthe chambers are maintained even under operating conditions and whichallows longer lengths to be economically produced.

Pursuant to this object, and others which will become apparenthereafter, one aspect of the present invention resides in a method ofmanufacturing a hollow spindle by providing an outer tube, forming aninner tube having a circumference with an inwardly curved region and acircular region, the inwardly curved region being configured to passinto the circular region in a rounded, stepless manner, sliding theinner tube into the outer tube, cold drawing the outer tube onto theinner tube, heat treating the inner tube and the outer tube in areducing atmosphere, adding a soldering agent, and final annealing thetubes to melt the soldering agent and fix the inner tube to the outertube so that two liquid-carrying chambers are formed.

The hollow spindle produced according to the present invention that isdistinguished by the fact that, instead of an inserted shaped section, ashaped inner tube rigidly connected to the outer tube by virtue of itsmaterial is used to form two chambers. The shaped inner tube, seen incross-section, has an inwardly curved region. The inwardly curved regionmakes a rounded and stepless transition to the circular region. The twochambers are sealed by a soldered layer, which is provided over theentire circumferential area of the inner surface of the outer tube thatcomes to rest against the inner tube, as well as over the outer surfaceof the inner tube. Both the outer tube and the inner tube are preferablymade of steel. However, other materials are also conceivable, such asCu, Al and combinations with steel. In many cases, a hollow spindle thatis used as a rocker lever spindle must be partially subjected toinduction hardening. In these cases, the outer tube is preferably madeof heat-treated steel.

The advantage of the method according to the invention is that theshaped inner tube can be economically drawn or rolled, whereas theinserted profile according to the prior art must be produced in anexpensive extrusion process. Because a soldered layer is applied to theentire circumference that comes to rest, the requisite impermeability ofthe chambers is ensured. The cold drawing of tubes placed one inside theother serves to draw the tubes one atop the other in a rattle-proofmanner. It is important, when this is done, that the two metal surfacesbeing pressed together be as metallically bare as possible and have noforeign particles between them. This is achieved by bright-annealingboth the outer tube and the inner tube in a reducing atmosphere prior toputting the two tubes together. In addition, this heat treatment may bepreceded by a degreasing process to ensure that no lubricant crackingresidues remain on the surface. To ensure that the inner tube, exceptfor its inwardly curved region, comes to rest against the circumferenceof the outer tube, the curved region should not have an overly acuteangle. A minimum opening angle of 60° and a minimum curvature radius of2.5 mm have proved advantageous for the curved region. Otherwise, theresilience of the curved region is too great, despite the support of aninternal die, and a certain portion of the transitional area does notcome to rest.

In order to keep the chambers tightly sealed, as mentioned above, theinner surface of the outer tube and the outer surface of the inner tubeare provided with an intervening soldered layer. For this purpose, themantle surface of the inner tube can be galvanically copper coated priorto the tubes being placed together, for example. Alternatively, it isalso possible to apply soldering paste or enclose the inner tube in asoldering foil or sprinkle soldering powder on the bare surface. Thislast method can be further supported by electrostatic charging. Theactual soldering is then carried out by means of annealing after thecold drawing. This annealing may be a heat treatment that would beneeded after cold drawing, or it may be an annealing during the courseof induction hardening. In addition or alternatively, the gap in thetransitional area between the curved region of the inner tube and thesupporting region of the outer tube can be filled with solder. For thispurpose, a soldering wire, especially made of copper, is placed into thesmaller chamber formed by the inner tube, and the tube is then annealed.The high temperature (in the range of 1100° C.) needed for annealingwhen a hard solder of Cu is used can lead, depending on the grade ofsteel, to coarse grain growth. To largely eliminate this phenomenon,that a normalizing annealing is carried out after soldering.Alternatively, it is also possible to use silver solder with a lowmelting point, so that the annealing for soldering purposes correspondsto a standard final heat treatment at approximately 950° and there is nodanger of coarse grain growth. The higher costs associated with thesilver solder are balanced by the elimination of further heat treatment.It should be noted that when silver solder is used, a flux material isoften necessary. Depending on how a particular hollow spindle is to beused, this is often undesirable, because the residues of the flux agentcan lead to unwanted chemical reactions.

The manufacture of a hollow spindle according to the invention isdescribed in greater detail below in reference to an example. In thisexample, the hollow spindle has an outer diameter of 24 mm and a wallthickness of 5.0 mm.

EXAMPLE

Starting from a cold-finished outer tube of heat-treatment st e.g., Ck45, having an outer diameter (Da A) of 26.1 mm and a wall thickness of3.8 mm the outer tube is subjected to normalizing annealing in areducing atmosphere. Parallel to this, a shaped inner tube of structuralsteel, e.g., St 35, having an outer diameter (Da I) of 17.5 mm and awall thickness of 1.7 mm is produced by cold drawing. The inner tube isalso subjected to heat treatment in a reducing atmosphere. Before theinner tube is placed into the outer tube, the outer surface of the innertube is galvanically copper coated. The inner tube is then inserted intothe outer tube and a drawing point is formed. To ensure that the(already formed) curvature of the inner tube rests against the outertube, beginning at the transitional area, with the fewest possibleinterruptions, a suitable internal die is used for support during colddrawing. For inner lubrication, a certain amount of lubricant isdeposited in the inner tube. For outer lubrication, circulatinglubrication is used. After the cold drawing, the hollow spindle that hasbeen created has an outer diameter of 24 mm and a total wall thicknessof 5 mm. In order to join the two tubes that are drawn together inrattle-proof fashion in a material locking fashion, the hollow spindleis annealed at 1100° C. for the purpose of soldering. In addition, asoldering wire can be placed in the chamber formed by the curvature, inorder to ensure that the interstitial area in the transitional region ofthe curvature and the circular inner tube is also filled with solder. Ifnecessary, a final normalizing treatment can be carried out to eliminateany coarse grain that may have formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a hollow spindle produced by the inventivemethod.

FIG. 2 is a cross-section of a hollow spindle produced by a prior artmethod.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In cross-section, FIG. 1 shows a finished hollow spindle based on theinventive manufacturing method. The hollow spindle has an outer tube 1of a heat-treatment steel Ck 45, for example, and a shaped inner tube 2of St 35, for example. As described above, the two tubular bodies havebeen cold drawn one atop the other in a rattle-proof fashion. The shapedinner tube 2, together with the outer tube 1, forms two chambers 3, 4.The cross-section of the smaller chamber 4 is limited by an innercircumferential area of the outer tube 1 and an outer circumferentialarea of the inward curvature 5 of the inner tube 2. The curved region 5passes in rounded fashion into the circular region 6 of the inner tube3. In the ideal case, this circular region 6 comes completely to restagainst the inner side of the outer tube 1. The actual extent of contactis heavily influenced by the nature of the curvature 5. The curvature 5should not have too sharp an angle or be insufficiently rounded. Anopening angle 7 of at least 60° and a curvature radius R₁ of at least2.5 mm have proved advantageous for the curvature. The rounding radiusR₂ in the curvature transitional region should be no smaller than 0.5mm. Otherwise, because of the resilience of the curvature 5, the dangerexists that the transitional area 8 will not come to rest. When thehollow spindle is to be used as a rocker lever spindle to controlexhaust-and-intake valves, the chambers 3, 4 are bored at differentlocations. This requires the seal between the chambers 3, 4 to be asfree of gaps as possible.

The proposed material connection between the inner tube 2 and the outertube 1 has the advantage that the total wall, i.e., the wall of theouter tube 1 plus the wall of the inner tube 2, can be taken intoaccount in calculating the carrying capacity of the hollow spindle. Thispermits the wall thickness of the outer tube 1 to be reduced and resultsin corresponding savings in weight. The rib to increase rigidity usuallyprovided in the prior art can therefore be omitted.

We claim:
 1. A method of manufacturing a hollow spindle, comprising thesteps of:providing an outer tube; forming an inner tube having acircumference with an inwardly curved region and a circular region, theinwardly curved region being configured to pass into the circular regionin a rounded, stepless manner; sliding the inner tube into the outertube; cold drawing the outer tube onto the inner tube; heat treating theinner tube and the outer tube in a reducing atmosphere; adding asoldering agent; and final annealing the tubes to melt the solderingagent and fix the inner tube in the outer tube so that twoliquid-carrying chambers are formed.
 2. A method as defined in claim 1,wherein the forming step includes shaping the inner tube by colddrawing.
 3. A method as defined in claim 1, wherein the forming stepincludes shaping the inner tube by cold rolling.
 4. A method as definedin claim 1, and further comprising the step of coating an outer surfaceof the inner tube with one of an element and alloy from the groupconsisting of copper, silver and gold, prior to the sliding step.
 5. Amethod as defined in claim 1, wherein the cold drawing step includessupporting the inner tube shape with an internal die.
 6. A method asdefined in claim 1, wherein the step of adding soldering agent includes,prior to the final annealing step, inserting a solder wire into asmaller of the chambers formed by the inner tube.
 7. A method as definedin claim 1, and further comprising the step of, after the solderingagent adding step, subjecting at least a section of the hollow spindleto a normalizing annealing.
 8. A method as defined in claim 7, whereinthe normalizing annealing step includes subjecting the entire hollowspindle to normalizing annealing.